Radioactive waste storage system and method

ABSTRACT

A system and method for storing radioactive waste, wherein the waste is placed in receptacles and the receptacles are moved selectively along a plurality of storage paths. The receptacles are retained selectively on said paths for periods of time dependent upon the periods required for the radioactivity of the waste therein to decay to predetermined levels.

1 3 "r a Unites; States ate [151 3,663,817 Sayers [4 1 May 16, 1972 [541 RADIOACTIVE WASTE STORAGE 3,257,561 6/1966 Packard et a1. ..250/106 sc T ND SYS EM A METHOD OTHER PUBLICATIONS [72] Invent Sayers Radioisotopes in industry, edited by John R. Bradford, Rein- [73] Assignee: FMC Corporation, San Jose, Calif. hold Publishing Corp. 1953 page 253 and 254 [22] Filed: July 1969 Primary Examiner-Archie R. Borchelt [2]] Ap l. No; 845,360 Attorney-F. W. Anderson and C E. Tripp Y [57] ABSTRACT [521 US. Cl. ....250/l06, 193/1, 193/2 R I 51 Int. Cl. ..G2lh 5/00 A System and method for Storms radwacllvc waste, wherein 58 Field of Search ..2so/52 106 so 193/1 2 the Waste is Placed in receptacles and receptacles are moved selectively along a plurality of storage paths. The [56} References Cited receptacles are retained selectively on said paths for periods of time dependent upon the periods required for the radioac- UN ST E PA S tivity of the waste therein to decay to predetermined levels.

2,751,505 6/1956 Anderson ..250/52 X 26 Claims, 4 Drawing Figures Patented May 16, 1972 4 Sl100ts-Shuet w. X @fifi KER Mix? WEN w XRX INVENTOR. ROBERT P. 5&YERS

ATTORNEYS Patented 4 Sheets-Sheet &

m: N m o RADIOACTIVE WASTE STORAGE SYSTEM AND METHOD BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to material storage systems and methods, and specifically to a system and method for storing radioactive waste.

2. Description of the Prior Art The radioactive waste from a nuclear reactor generally contains isotopes having various half-lives. The decay periods for these isotopes vary from a few microseconds to several years. However, many of the most active isotopes have decay periods of a few years, for example, 4-6 years.

The amount of shielding required to effectively encase the waste after the more active isotopes have decayed is much less than that required before such isotopes have decayed. Thus, it is much more economical to dispose of radioactive waste in a permanent manner, as by storage in an underground cavity or by reprocessing it after the more active isotopes have decayed due to the reduced shielding required. In order to permit radioactive waste to be disposed of in this manner, however, a system must be provided for storing the waste during the period required for the more active isotopes to decay. Such a system must include a shielded storage space and means for introducing and removing the waste from such space. Also, the system should include means which permit the waste to be stored for varying periods of time dependent upon the composition and radioactivity level of the particular waste being stored.

Systems for accomplishing one or more of the foregoing functions are known in which radioactive waste is transported into, through and from a storage space at controlled rates of movement by powered conveying and/or lifting equipment. Generally, such systems include complex electrical and mechanical devices and occupy a relatively large space. Systems of this type are not only relatively expensive to install but are susceptible to breakdowns, thus posing a hazard to personnel safety.

SUMMARY OF THE INVENTION The storage system and method of the present invention provides an optimum solution to the problem of storing radioactive waste for the period required for the more active isotopes contained in the waste to decay. The system is relatively simple and rugged, and therefore is capable of operating for several years without breakdowns. Also, the space occupied by the system is employed in an efficient manner, thus minimizing installation cost.

Basically described, the system of the invention comprises; a plurality of elongated storage racks; a plurality of carriages movable along the racks, said racks each having a carriagereceiving end and a carriage-discharge end; means for loading radioactive waste onto the carriages individually; means for selectively placing the carriages onto or removing them from the carriage-receiving ends; means for moving the carriages along the racks from the carriage-receiving to the carriagedischarge ends thereof and vice versa, whereby the carriages may be retained selectively on the racks for predetermined periods of time dependent upon the periods required for the radioactivity of the waste thereon to decay to predetermined levels; means for selectively receiving the carriages from or placing them onto the carriage-discharge ends; and means for unloading radioactive waste from the carriages individually.

The means for moving the carriages along the racks preferably comprises the racks being inclined downwardly from the carriage-receiving to the carriage-discharge ends thereof so that the carriages are moved along the racks by gravitational force. However, the racks may be horizontal and the carriages moved therealong by power means preferably disassociated from the carriages.

The method of the invention may be performed by the foregoing system and basically comprises; placing radioactive waste in receptacles; and moving the receptacles selectively along a plurality of storage paths, the receptacles being retained selectively on said paths for periods of time dependent upon the periods required for the radioactivity of the waste to decay to predetermined levels.

Preferably, the storage paths are defined by the aforementioned elongated storage racks.

With the foregoing in mind, it is an object of. the present invention to provide an improved system and method for storing radioactive waste.

It is also an object of the invention to provide a system and method for storing radioactive waste in which the waste is transported into, through, and from a storage space in an effcient and safe manner.

It is a further object of the invention to provide a system and method for storing radioactive waste in which the waste may be retained selectively for predetermined periods of time dependent upon the radioactivity level thereof.

It is an additional object of the invention to provide a system for storing radioactive waste, which system is relatively simple and rugged, and is capable of operating for many years without breakdowns.

It is still another additional object to provide a system for storing radioactive waste, wherein individual material carrying carriages can be removed and repaired without impairing or tying up an entire line of such carrying carriages.

These and other objects of the invention will become apparent upon a consideration of the detailed description of the preferred embodiments thereof given in connection with the following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic plan view of the radioactive waste storage system of the invention.

FIG. 2 is a vertical section taken substantially along lines 22 of FIG. 1.

FIG. 3 is a vertical section taken substantially along lines 33 of FIG. 1.

FIG. 4 is a vertical longitudinal section of an alternative embodiment of the system shown in FIGS. 1 to 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiment of the system of the invention is shown in the drawings, as designated by reference numeral 10. System 10 includes an enclosure 12 defined by a plurality of external shielding walls 13. The enclosure is divided into a plurality of storage bays, such as bays I4 and 16, by internal shielding walls 18. A control and observation booth 20 is provided adjacent one side of the enclosure 12 and is shielded from the interior of the enclosure by suitable transparent shielding 22 through which an operator may observe and control the operations occurring within the enclosure.

A plurality of elongated racks 24 are positioned within each of the bays 14 and 16. The racks are arranged in side-by-side rows of vertically stacked groups, and are supported by a plurality of stanchions 25.

System 10 also includes a plurality of carriages 26 which are movable along racks 24 from carriage-receiving ends 28 to carriage-discharge ends 30 of the racks. Each carriage 26 includes a plurality of supporting wheels 32 which are engageable with means mounted on racks 24, such as tracks 34, for guiding the carriages along the racks.

Means are provided for moving carriages 26 from carriagereceiving ends 28 to carriage-discharge ends 30. In the embodiment of the system shown in FIGS. 1 to 3 of the drawings such means comprise racks 24 being inclined downwardly from ends 28 to ends 30 so that carriages 26 are moved along the racks by gravitational force. Alternately, as shown in FIG. 4 and discussed in more detail below, racks 24 may be horizontally disposed and suitable powered means, such as pneumatic or hydraulic piston devices, provided for moving the carriages along the racks.

Means are also provided for loading radioactive waste containers onto and unloading radioactive waste containers from carriages 26. Such loading and unloading means conveniently include a plurality of receptacles 36. Radioactive waste from a nuclear reactor is introduced into receptacles 36 individually at a receptacle filling and emptying station 38 adjacent control booth 20. Suitable means (not shown) are provided for delivering the waste from the reactor to station 38. The loading and unloading means also include a conventional overhead travelling crane 40 mounted in the storage bay 14. The crane 40 lifts the filled receptacles individually from station 38 and loads the receptacles onto carriages 26.

Means are further provided for positioning carriages 26 for receiving receptacles 36 thereon and for placing the receptacles onto carriage-receiving ends 28 of racks 24. Such means include a travelling elevator 42 positioned adjacent ends 28. Elevator 42 includes a plurality of supporting wheels 44 which engage tracks 46 extending transversely of racks 24 adjacent ends 28. One or more of wheels 44 is driven by suitable powered means so that elevator 42 may be moved from adjacent station 38 to adjacent the carriage-receiving ends 28 of a selected vertical group of racks 24. Of course, other means for driving the elevator could be utilized such as a double rope or chain haul system, or any reliable means suitable for moving the device back and forth along tracks 46. Elevator 42 also includes a vertically movable lift 48 on which one of carriages 26 is adapted to be supported for receiving one of the receptacles 36 thereon preparatory to placement of the carriage onto one of the ends 28. Attached to lift 48 is a carriage-shifting mechanism, such as pneumatic or hydraulic piston and cylinder device 50, for pushing each carriage from the lift onto one of the ends 28. The carriage-shifting mechanism is not to be limited as such, however, as an electro-mechanical actuator, an all mechanical device such as reciprocating or oscillating sweep arms, or a chain with pusher dogs could also be used.

Each carriage 26 includes a structural framework 52 for holding a filled receptacle 36 with the gravitational center of the receptacle in proximity to or below a line extending longitudinally of the carriage and passing through the geometric center of a polygon formed by the lines joining the gravitational centers of the wheels 32 of the carriage. The filled receptacle is thus held by framework 52 in an extremely stable position, minimizing the possibility of the receptacle tipping over.

After a particular carriage 26 has been placed onto the carriage-receiving end 28 of one of racks 24, the carriage is moved along the rack by gravitational force until it reaches carriage-discharge end 30 of the rack. Preferably, a plurality of carriages are moved along each rack 24 simultaneously so that a train of carriages extends from end 28 to end 30 of each rack either in a loaded or empty state.

Each carriage 26 is retained on the selected rack 24 until the radioactivity of the waste within the receptacle 36 loaded on the carriage has decayed to a predetermined level, and preferably until the more active isotopes within the waste have decayed. The carriage is then discharged from the rack. Means are provided for releasing only one carriage at a time from each of carriage-discharge ends 30. Such means conveniently comprise an escapement mechanism 54 mounted adjacent each end 30. Upon the actuation of one of mechanisms 54, the carriage adjacent the associated end 30, and only that carriage, is discharged from the associated rack.

Means are also provided for receiving carriages 26 when the carriages are released from ends 30. Such means comprise a travelling elevator 56 which is similar to elevator 42, including a plurality of supporting wheels 58, one or more of which are driven by suitable powered means, and a vertically movable lift 62 on which one of carriages 26 is adapted to be supported. Wheels 58 engage tracks 60 which extend transversely of racks 24 adjacent ends 30.

Prior to the release of a carriage 26 from one of carriagedischarge ends 30, lift 62 is positioned for receiving the carriage thereon. Upon the actuation of the appropriate escapement mechanism 54, the carriage rolls from the carriagedischarge end 30 onto lift 62 of the elevator 56. The elevator is then moved transversely of racks 24 until it is adjacent station 38 at which point the receptacle loaded on the carriage is unloaded therefrom by crane 40 and placed at station 38. The radioactive waste within the receptacle is then removed therefrom by suitable means (not shown) to be transported to a site for permanent disposal or for reprocessing. Since the elevators 42 and 56 are movable into both of the bays 14 and 16, only one filling and emptying station 38 and one travelling crane 40 are required for servicing both bays.

System 10 also includes means for moving carriages 26 from the carriage-discharge ends 30 to the carriage-receiving ends 28, Le, for moving unloaded carriages back to elevator 46 for receiving freshly filled receptacles thereon. Such means include a carriage-shifting mechanism, such as a pneumatic or hydraulic piston and cylinder device 64 or any other suitable device, attached to lift 62, and one or more return-racks 68. In the embodiment shown in the drawings, a return-rack 68 is provided in each of the bays 14 and 16 adjacent the internal wall 18 separating the bays. The unloaded carriages 26 are pushed from the lift 62 onto return-racks 68 by the device 64.

Means are also provided for moving carriages 26 along return-racks 68. In the embodiment shown in FIGS. 1 to 3 of the drawings, this latter means comprises the return-racks being inclined from the' carriage-discharge ends 30 downwardly to the carriage-receiving ends 28 so that the carriages are moved along the return-racks by gravitational force. Alternatively, as shown in FIG. 4, the return-racks may be substantially horizontally disposed, as discussed below, and suitable powered means provided for moving the carriages along the racks. Suitable escapement mechanisms (not shown) are associated with return-racks 68 for releasing the carriages individually onto platform 48 as required for receiving freshly filled receptacles 36 thereon.

In the alternative embodiment, as shown in FIG. 4 wherein like parts are designated with like reference numerals followed by the suffix a," the racks 24a are horizontally disposed. Since the carriages will not roll down the horizontal racks under gravitational force, other means must be utilized for advancing the carriages from the carriage-receiving end 28a to the carriage-discharge end 30a or vice versa. One simple and reliable way to so advance the carriages is to maintain all the racks in a fully occupied state, then by chain reaction the insertion of an additional carriage 26a into a rack 240 will cause the ejection of a carriage from the opposite end. This embodiment of the invention is also provided with an additional escapement mechanism 54a at the carriage-receiving end 28a of the system to prevent a carriage from possibly rolling off its rack 24a when the elevator 42a is not there to receive it.

Because of the horizontal disposition of the racks, any one or a plurality of the racks can be used as return-racks 68a. They operate the same as the forwardly carrying racks 24a only in a reverse direction so that a carriage which is being returned to the receiving end 28a of the system is inserted into one of the return racks 68a by elevator 56a and carriage shifting mechanism 640 and simultaneously a carriage is ejected from the opposite end of the rack 68a and received by elevator 42a.

It is to be noted that with either embodiment, damaged carriages can be taken from either end of the fully occupied racks so that they can be removed from the system at station 38 and repaired outside the system. The removal of such a carriage will not disrupt the functioning of the system, however, as a spare carriage can be put in the system to replace the damaged carriage.

Also, as shown in the embodiment of FIG. 4, a radioactive material detector 72a, such as a geiger counter, could be placed in the system on the receiving elevator 56a to monitor the remaining radioactivity in each container at the end of its storage period as it is pushed onto the elevator. If the radioactivity is still too high, the carriage and the radioactive material could be recycled back to the receiving end of the system for resubmission onto a storage rack for further decay. Of course, such a detector could also be used in the system disclosed in FIGS. 1 to 3.

It is contemplated that the entire system could be automated with each carriage coded and assigned a particular decay rack every time it is provided with a new container of radioactive material. The amount of radioactivity remaining in the material could be automatically monitored by detector 72a as the carriages are taken from the discharge end of the racks, and depending on the remaining radioactivity, either automatically recycled or removed from the system.

Depending upon the amount of waste required to be stored from a particular nuclear reactor, enclosure 12 may include additional storage bays beneath bays l4 and 16, such as bay 70, in which waste handling equipment similar to that described above is installed.

One of the principal advantages of system is the storage flexibility that the system provides. Frequently, the radioactive waste from a reactor will have different compositions and levels of radioactivity. Thus, it is desirable that means be provided for storing different quantities of the waste for different periods of time. This result is made possible by system 10. One ore more racks 24 may be allocated for the retention of particular quantities of waste requiring a particular storage period, while other racks may be allocated for the retention of other quantities of waste requiring different storage periods. By thus assigning each receptacle to a rack on which waste having a similar storage period is retained, several storage periods may be provided, thus avoiding the undesirable alternatives of either retaining a particular quantity of waste longer than required or attempting to remove a particular carriage from the middle of a train of carriages extending along one of the racks.

In operation the carriages may be removed from and loaded onto the racks at regular intervals, such that when one carriage is released from the carriage-discharge end of a rack, a newly loaded carriage is placed onto the carriage-receiving end of the same rack. This process is repeated periodically, so that each carriage is moved down one of the racks intermittently during the required storage period.

The method of the invention will be apparent from the foregoing description of the system of the invention, including placing radioactive waste into receptacles and moving the receptacles selectively along a plurality of storage paths; the paths preferably being defined by racks 24. The receptacles are retained selectively on the storage paths for periods of time dependent upon the periods required for the radioactivity of the waste therein to decay to predetermined levels. As described above, preferably a plurality of carriages are simultaneously and intermittently moved along each of the paths.

The system and method of the invention comprise a highly efficient and safe manner for storing radioactive waste. In par ticular, the system comprises a relatively simple and rugged structure, and is designed to operate for many years without breakdowns. The system therefore requires a minimum of maintenance and attention, and thus minimizes the possibility of personnel exposure to harmful radiation. Also, the space occupied by the system is optimumly employed, thus minimizing installation cost.

The foregoing constitutes a detailed description of the system and method of the invention. It is recognized, however, that within the scope of the invention various modifications will occur to those skilled in the art.

I claim:

I. A system for storing radioactive waste comprising a plurality of carriers adapted to receive and temporarily store the waste, means defining a plurality of pathways inclined downwardly from an entrance end to a discharge end along which said carriers can move, each pathway having a predetermined length whereby movement of a carrier from one end of the pathway to the other at a particular speed involves a predetermined amount of decay of the waste.

2. The system of claim 1 including means for recycling said carriers along said pathways as desired.

3. The system of claim 2 wherein said recycling means includes tracks inclined in a direction to move carriers by gravity in a direction contra to the direction they move along said pathways.

4. A system for storing radioactive waste comprising: a plurality of elongated storage racks; a plurality of carriages movable along said racks, said racks each having a carriage-receiving end and a carriage-discharge end; means for loading radioactive waste onto said carriages individually; means for selectively placing said carriages onto said carriage-receiving ends; said carriages being movable along said racks from the carriage-receiving to the carriage-discharge ends thereof, whereby the carriages may be retained selectively on the racks for predetermined periods of time dependent upon the periods required for the radioactivity of the waste thereon to decay to predetermined levels; means for selectively receiving said carriages from said carriage-discharge ends; and means for unloading radioactive waste from said carriages individually.

5. A system as recited in claim 4, wherein said loading and unloading means include a plurality of receptacles adapted to be filled with radioactive waste and a crane for individually loading said receptacles onto and unloading said receptacles from said carriages.

6. A system as recited in claim 5 wherein each of said carriages includes a plurality of wheels; and wherein said system further includes means mounted on each of said racks and engageable with said wheels for guiding the carriages along the racks.

7. A system as recited in claim 6, wherein each of said carriages further includes means for holding one of said receptacles filled with waste with the gravitational center of the receptacle in proximity to or below a line extending longitudinally of the carriage and passing through the geometric center of a polygon formed by lines joining the gravitational centers of the wheels of the carriage.

8. A system as recited in claim 4, wherein said racks are inclined downwardly from the carriage-receiving to the carriage-discharge ends thereof so that the carriages are moved along the racks by gravitational force.

9. A system as recited in claim 8, further comprising means for releasing only one carriage at a time from each of said carriage-discharge ends.

10. A system as recited in claim 9, wherein said releasing means comprises an escapement mechanism associated with each of said carriage-discharge ends.

11. A system as recited in claim 4, wherein said placing means comprises; an elevator positioned adjacent said racks for individually positioning said carriages adjacent said carriage-receiving ends, and a carriage-shifting mechanism attached to said elevator for individually moving the carriages from the elevator onto the carriage-receiving ends.

12. A mechanism as recited in claim 4, wherein said receiving means comprises an elevator positioned adjacent said racks for individually receiving said carriages from said carriage-discharge ends.

13. A system as recited in claim 12, wherein said means for moving said carriages from said carriage-discharge ends to said carriage-receiving ends includes at least one additional rack extending from adjacent said carriage-discharge ends to adjacent said carriage-receiving ends, a carriage-shifting mechanism mounted on said elevator for individually moving the carriages from the elevator onto said one additional rack, and means for moving the carriages along said one additional rack.

14. A method for storing radioactive waste comprising the steps of placing said waste in receptacles; moving said receptacles selectively along a plurality of storage paths; and retaining said receptacles selectively on said paths for periods of time dependent upon the periods required for the radioactivity of said waste to decay to predetermined levels.

15. A method as recited in claim 14, further comprising the steps of moving a plurality of receptacles along each of said paths simultaneously.

16. A method as recited in claim 14, wherein said receptacles are intermittently moved along said paths.

17. The system of claim 1 wherein said pathways include tracks which are horizontally disposed.

18. The system of claim 2 wherein said recycling means include horizontally disposed tracks.

19. A system for storing radioactive waste comprising: a plurality of elongated storage racks having two ends; a plurality of carriages movable along said racks; means for loading radioactive waste onto said carriages individually; means for selectively placing said carriages onto either end of said storage racks; means for moving said carriages along said racks whereby the carriages may be retained selectively on the racks for predetermined periods of time dependent upon the periods required for the radioactivity of the waste thereon to decay to predetermined levels; means for selectively receiving said carriages at either end of said racks; and means for unloading radioactive waste from said carriages individually.

20. A system as recited in claim 19, further comprising means at both ends of said racks for either releasing only one carriage at a time from said racks or for receiving only one carriage at a time onto said racks.

21. A system are recited in claim 20, wherein said releasing and receiving means comprises an escapement mechanism associated with each end of said racks.

22. A method of storing radioactive waste in an enclosure having a plurality of storage paths arranged in side-by-side rows of vertically stacked groups and at least one return path, comprising the steps of placing said waste in receptacles; transporting said receptacles traversingly along said rows of storage paths at one end thereof to a preselected row; elevating said receptacles to a preselected storage path in said preselected row; placing said receptacles into said preselected storage path; and moving said receptacles selectively along said storage path until they reach the opposite ends of said paths.

23. A method as recited in claim 22, further comprising the step of removing said receptacles from said enclosure after they have reached said opposite ends of said storage paths.

24. A method as recited in claim 22, further comprising the steps of removing said receptacles from said opposite ends of said storage paths; transporting said receptacles to said return path; placing said receptacles on said return path at said opposite end; and then recycling said receptacles by removing them from said return path at said one end and replacing them in said storage paths.

25. A method as recited in claim 23, further comprising the step of monitoring the radioactivity of said waste upon its reaching said opposite ends of said storage paths.

26. A method as recited in claim 24, further comprising the step of monitoring the radioactivity of said waste upon its reaching said opposite ends of said storage paths. 

1. A system for storing radioactive waste comprising a plurality of carriers adapted to receive and temporarily store the waste, means defining a plurality of pathways inclined downwardly from an entrance end to a discharge end along which said carriers can move, each pathway having a predetermined length whereby movement of a carrier from one end of the pathway to the other at a particular speed involves a predetermined amount of decay of the waste.
 2. The system of claim 1 including means for recycling said carriers along said pathways as desired.
 3. The system of claim 2 wherein said recycling means includes tracks inclined in a direction to move carriers by gravity in a direction contra to the direction they move along said pathways.
 4. A system for storing radioactive waste comprising: a plurality of elongated storage racks; a plurality of carriages movable along said racks, said racks each having a carriage-receiving end and a carriage-discharge end; means for loading radioactive waste onto said carriages individually; means for selectively placing said carriages onto said carriage-receiving ends; said carriages being movable along said racks from the carriage-receiving to the carriage-discharge ends thereof, whereby the carriages may be retained selectively on the racks for predetermined periods of time dependent upon the periods required for the radioactivity of the waste thereon to decay to predetermined levels; means for selectively receiving said carriages from said carriage-discharge ends; and means for unloading radioactive waste from said carriages individually.
 5. A system as recited in claim 4, wherein said loading and unloading means include a plurality of receptacles adapted to be filled with radioactive waste and a crane for individually loading said receptacles onto and unloading said receptacles from said carriages.
 6. A system as recited in claim 5 wherein each of said carriages includes a plurality of wheels; and wherein said system further includes means mounted on each of said racks and engageable with said wheels for guiding the carriages along the racks.
 7. A system as recited in claim 6, wherein each of said carriages further includes means for holding one of said receptacles filled with waste with the gravitational center of the receptacle in proximity to or below a line extending longitudinally of the carriage and passing through the geometric center of a polygon formed by lines joining the gravitational centers of the wheels of the carriage.
 8. A system as recited in claim 4, wherein said racks are inclined downwardly from the carriage-receiving to the carriage-discharge ends thereof so that the carriages are moved along the racks by gravitational force.
 9. A system as recited in claim 8, further comprising means for releasing only one carriage at a time from each of said carriage-discharge ends.
 10. A system as recited in claim 9, wherein said releasing means comprises an escapement mechanism associated wiTh each of said carriage-discharge ends.
 11. A system as recited in claim 4, wherein said placing means comprises; an elevator positioned adjacent said racks for individually positioning said carriages adjacent said carriage-receiving ends, and a carriage-shifting mechanism attached to said elevator for individually moving the carriages from the elevator onto the carriage-receiving ends.
 12. A mechanism as recited in claim 4, wherein said receiving means comprises an elevator positioned adjacent said racks for individually receiving said carriages from said carriage-discharge ends.
 13. A system as recited in claim 12, wherein said means for moving said carriages from said carriage-discharge ends to said carriage-receiving ends includes at least one additional rack extending from adjacent said carriage-discharge ends to adjacent said carriage-receiving ends, a carriage-shifting mechanism mounted on said elevator for individually moving the carriages from the elevator onto said one additional rack, and means for moving the carriages along said one additional rack.
 14. A method for storing radioactive waste comprising the steps of placing said waste in receptacles; moving said receptacles selectively along a plurality of storage paths; and retaining said receptacles selectively on said paths for periods of time dependent upon the periods required for the radioactivity of said waste to decay to predetermined levels.
 15. A method as recited in claim 14, further comprising the steps of moving a plurality of receptacles along each of said paths simultaneously.
 16. A method as recited in claim 14, wherein said receptacles are intermittently moved along said paths.
 17. The system of claim 1 wherein said pathways include tracks which are horizontally disposed.
 18. The system of claim 2 wherein said recycling means include horizontally disposed tracks.
 19. A system for storing radioactive waste comprising: a plurality of elongated storage racks having two ends; a plurality of carriages movable along said racks; means for loading radioactive waste onto said carriages individually; means for selectively placing said carriages onto either end of said storage racks; means for moving said carriages along said racks whereby the carriages may be retained selectively on the racks for predetermined periods of time dependent upon the periods required for the radioactivity of the waste thereon to decay to predetermined levels; means for selectively receiving said carriages at either end of said racks; and means for unloading radioactive waste from said carriages individually.
 20. A system as recited in claim 19, further comprising means at both ends of said racks for either releasing only one carriage at a time from said racks or for receiving only one carriage at a time onto said racks.
 21. A system are recited in claim 20, wherein said releasing and receiving means comprises an escapement mechanism associated with each end of said racks.
 22. A method of storing radioactive waste in an enclosure having a plurality of storage paths arranged in side-by-side rows of vertically stacked groups and at least one return path, comprising the steps of placing said waste in receptacles; transporting said receptacles traversingly along said rows of storage paths at one end thereof to a preselected row; elevating said receptacles to a preselected storage path in said preselected row; placing said receptacles into said preselected storage path; and moving said receptacles selectively along said storage path until they reach the opposite ends of said paths.
 23. A method as recited in claim 22, further comprising the step of removing said receptacles from said enclosure after they have reached said opposite ends of said storage paths.
 24. A method as recited in claim 22, further comprising the steps of removing said receptacles from said opposite ends of said storage paths; transporting said receptacles to said return path; placing said receptacles on said return path aT said opposite end; and then recycling said receptacles by removing them from said return path at said one end and replacing them in said storage paths.
 25. A method as recited in claim 23, further comprising the step of monitoring the radioactivity of said waste upon its reaching said opposite ends of said storage paths.
 26. A method as recited in claim 24, further comprising the step of monitoring the radioactivity of said waste upon its reaching said opposite ends of said storage paths. 